1. Field of the Invention
The present invention relates to a combination refrigeration circuit and supplemental heating means. More specifically, this invention relates to integration of the controls of a refrigeration circuit with a supplemental heating means to prevent simultaneous operation of both.
2. Prior Art
In order to most effectively supply heating to many enclosures a reverse cycle refrigeration circuit or heat pump is often combined with a fossil fuel fired furnace. The combination of systems is then operated such that the heat pump is used to supply heat energy to a space to be conditioned when it is most economical to run the heat pump. The heat pump is then turned off and the furnace operated to supply heating to the enclosure when it is most economical to operate the furnace.
One of the potential problems of such a system is that the indoor air stream circulating air from the enclosure through the heating means typically flows over the heat exchangers of the furnace, then over the indoor heat exchanger of the refrigeration circuit serving as a condenser. If both systems were operated simultaneously the heated air is directed from the furnace heat exchangers to the condenser of the heat pump. Since this air will typically be a higher temperature than the operating design conditions of the condenser of a heat pump the condensing temperature and pressure would increase until a malfunction might occur in the heat pump system. Of course, the typical heat pump system would include a safety device to prevent overpressure conditions or high temperature operation.
The appropriate integration of the systems to prevent undue head pressures from occurring is known to be a desirable effect. The listing agencies for certifying air conditioning equipment have made it a requirement that an interlock device be provided such that simultaneous operation of the heat pump and the furnace, except in a defrost mode of operation, cannot happen.
Previous means of preventing simultaneous operation have included a switch for selecting either the heat pump heating mode or the furnace heating mode and having no provision where both may be operated. Other systems include providing a thermal sensing means in the air being supplied to the condenser for discontinuing heat pump operation should a sensing means detect a sufficiently high temperature indicating the furnace is operating.
The present invention concerns the integration of a microprocessor control into the operation of a combination heat pump and furnace system. Such a system herein is referred to as an optimizer system indicating that either the heat pump or the furnace may be operated as appropriate under the circumstances. As set forth herein, a specific terminal of the microprocessor control is energized to bring about operation of the furnace. Under the control logic the compressor is de-energized at that time. A separate logic scheme is provided to determine if the compressor is operating even though compressor operation is not being called for by the control. If this is the case then the operation of the furnace is prevented. In addition, the control determines if the furnace is operating and locks out the compressor to prevent simultaneous operation of both the heat pump and the furnace.